This invention generally relates to powering inductive loads such as coils in fuel injectors. More particularly, this invention relates to monitoring the current only on the high side of an inductive load to achieve a desired performance.
Fuel injectors are well known. Typical arrangements include a coil that is energized in a manner that allows for fuel supply to a vehicle engine according to a control strategy responsive to a driver manipulating an accelerator pedal, for example. Typical arrangements include a high side driver and a low side driver on opposite sides of the coil that is energized to control the fuel injector. A typical arrangement includes a shunt resistor associated with each driver so that the current on each side of the coil can be monitored.
Conventional arrangements require monitoring the current on both sides of the coil to achieve proper coil operation and to avoid over current situations. With conventional arrangements, the high side driver and low side driver are turned on when fuel injector operation is required. As the current in the coil rises to a maximum desired level, the high side driver typically is turned off and on in a cyclical manner to allow the current to cyclically rise and fall within a desired range. During this “chopping” using the high side driver, the coil is energized sufficient to allow fuel flow as needed. The low side driver typically remains on throughout the entire interval when the coil is energized. At the end of fuel injection operation the low side driver and the high side driver are turned off so the coil can be deenergized.
The current associated with the low side driver typically is monitored to provide information regarding the level of current in the coil. That provides information for operating the high side driver to achieve the chopping necessary to keep the coil current within desired limits.
The current on the high side typically is monitored to provide a failure protection mode to protect against a high side overcurrent situation.
Conventional arrangements have proven useful but have certain shortcomings and drawbacks. Conventional arrangements are relatively expensive because the operational amplifier needed for monitoring the current on the high side driver side of the coil typically is a relatively complicated device even though it is almost always never actually used for purposes of turning off current to the coil. Additionally, the circuitry required for achieving the necessary chopping with the high side driver is relatively complicated and occupies a large space on a circuit board. The overall size of the control module, therefore, becomes larger than may be desirable for some situations. Additionally, the conventional arrangement requires an amplifier and a comparator on both sides of the coil, which increases the number of parts and, again, keeps the size of the module relatively large. The additional weight of such control modules is another drawback. Further, conventional arrangements require increased testing, which increases cost, and tend to have potential reliability issues presented by the number of components required.
There is a need for an improved arrangement for powering inductive loads such as fuel injectors that does not suffer from the drawbacks and shortcomings mentioned above. This invention provides such an arrangement.